Larry R. D'Addario 
September 25, 1997
Keywords: cryogenics, refrigerator, compressor, Gifford-McMahon, GM
In this report, data is compiled on several commercially available cryocoolers that reach 4K by a two-stage Gifford-McMahon (GM) cycle. Some recent papers on these devices and experience at other radio observatories are discussed. Whereas there is so far no such experience at the NRAO, this information is aimed at deciding whether such devices are candidates for use on the Millimeter Array. Temperature stability and power consumption are major considerations.
Available devices do not closely match the assumed MMA requirements, and would produce little advantage in power consumption compared with three-stage GM/JT systems. But there may be advantages in simplicity and reliability. Modifications and adjustments may result in a power advantage. In-house experimental work is recommended, including tests of passive and active temperature stabilization techniques.
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